I installed Ubuntu 12.04 on my external USB drive, where I have a 700GB NTFS partition followed by the new 6GB ext4 partition and a swap partition (all primary). The GRUB MBR is also installed to the external hard disk.

Since my BIOS puts the external drive as first disk when booting, I removed my internal hard disk before installation in order to avoid ordering problems.

Now when I boot from the external drive, GRUB is stuck at the rescue console with the error "unknown filesystem".

grub rescue> ls
(hd0) (hd0,msdos3) (hd0,msdos2) (hd0,msdos1)

ls (hd0,<any of them>)/ gives me "unknown filesystem", thus also "insmod normal"

GRUB doesn't seem to be able to read my Linux partition as you can see above?! How can I solve this?

Additional info:

bootinfoscript says (this is with the internal drive in again, but that does not make a difference):

Grub2 (v1.99) is installed in the MBR of /dev/sdb and looks at sector 1 of the same hard drive for core.img. core.img is at this location and looks for (,msdos2)/boot/grub on this drive.

sdb1: __________________________________________________________________________

    File system:       ntfs
    Boot sector type:  Windows Vista/7: NTFS
    Boot sector info:  No errors found in the Boot Parameter Block.
    Operating System:  
    Boot files:        

sdb2: __________________________________________________________________________

    File system:       ext4
    Boot sector type:  -
    Boot sector info: 
    Operating System:  Ubuntu 12.04 LTS
    Boot files:        /boot/grub/grub.cfg /etc/fstab /boot/grub/core.img

sdb3: __________________________________________________________________________

    File system:       swap
    Boot sector type:  -
    Boot sector info: